Sense Organs

There are five senses: sight, hearing, taste, smell and touch. There are organs connected with these sense that take in information that is sent to the brain so that the body can act on it.

Sight

The eye is the organ of the sense of sight. Eyes detect light, and convert it to electro-chemical impulses in neurons.

Parts of the eye:

Cornea

The transparent window at the front of the eye which is covered in a thin layer of tears.

Aqueous humor

On the other side of the cornea is more moisture. This clear, watery fluid is the aqueous humor. It circulates throughout the front part of the eye and keeps a constant pressure within the eye.

Pupil and iris:

The pupil is the circular opening in the colored part of the eye which is the iris. The iris dilates or opens and contracts to let in more or less light.

Lens:

Resembles the lens of a camera and focuses the light, changing shape as it takes in light reflected from objects near and far.

Vitreous:

A clear jelly that the focused light passes through to the retina.

Retina:

The inner lining at the back of the eye. It contains blood vessels which bring nutrients to the nerve cells. The macula is at the very center of the retina and contains the fovea. The photoreceptors of the retina are the rods and cones. The cones perceive color and finer elements. The retinal pigment epithelium, choroid and sclera are three more layers. The photoreceptors send light and images to a large nerve called the optic nerve. This carries the information to the occipital lobe of the brain where they are interpreted.

Eyelids and eyelashes:

These protect the eye and along with tears keep the eye clear and moist.

Hearing

The ear is the organ concerned with hearing. The ear has three parts: the outer ear, the middle ear and the inner ear.

Outer ear:

Pinna:

The outermost part of the ear made of cartilage that is connected to the outer tube called the auditory canal. This leads to the eardrum.

Middle Ear

Eardrum, stirrup, anvil and hammer:

This membrane vibrates and along with the three tiny bones in the middle ear, the hammer, anvil and stirrup, and sends the stiumuli to the cochlea.

Inner Ear:

Cochlea:

Is spiral shaped and it transforms sound into nerve impulses that travel to the brain.

Semicircular canals:

These fluid filled tubes attach to the cochlea and nerves in the inner ear. They send information on balance and head position to the brain.

Eustachian tube:

Drains fluid from the middle ear into the throat behind the nose.

Taste:

Tongue:

Is a muscular organ in the mouth. The tongue is covered with moist, pink tissue called mucosa and tiny bumps called papillae. Thousands of taste buds cover the surfaces of the papillae. Taste buds are collections of nerve-like cells that connect to nerves going into the brain. There are four types of taste buds: sour, sweet, bitter and salty.

The tongue is vital in tasting and chewing food and in speech.

Smell:

Nose:

The nose, along with the mouth, lets air in and out of the body. It also helops us distinguish different smells in that air.

The nasal root is the top of the nose, forming an indentation at the suture where the nasal bones meet the frontal bone. The anterior nasal spine is the thin projection of bone at the midline on the lower nasal margin, holding the cartilaginous center of the nose.[1] Adult humans have nasal hairs in the anterior nasal passage.

Touch

Skin:

The skin is the largest organ of the body, with a total area of about 20 square feet. The skin protects us from microbes and the elements, helps regulate body temperature, and permits the sensations of touch, heat, and cold. The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone.

Layers:

The dermis, beneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands.
The deeper subcutaneous tissue (hypodermis) is made of fat and connective tissue.
The skin's color is created by special cells called melanocytes, which produce the pigment melanin. Melanocytes are located in the epidermis.